.loader {
    width: 400px;
    margin: 0 auto;

    span {
        display: inline-block;
        width: 20px;
        height: 20px;
        border-radius: 100%;
        background-color: #3498db;
        margin: 35px 5px;
        opacity: 0;

        &:nth-child(1) {
            animation: opacityChange 1s ease-in-out infinite;
        }

        &:nth-child(2) {
            animation: opacityChange 1s ease-in-out 0.2s infinite;
        }

        &:nth-child(3) {
            animation: opacityChange 1s ease-in-out 0.4s infinite;
        }

    }
}

@keyframes opacityChange {

    0%,
    100% {
        opacity: 0;
    }

    60% {
        opacity: 1;
    }
}